Re: Soil tests, Vermiculite, pH, KH & CO2

Re: Soil Tests (incl. laterite)

I found that soil test info (incl. laterite) very interesting but I'm 
wondering why iron content or index was not measured.  Also, did anyone
who has used Tetra Initial D notice a lowering of water pH when they
filled the aquarium with water since the pH is so low (3.8).  The authors
do not appear to consider Tetra Initial D a laterite - is this general
consensus.  And, where can you buy Aquarium Products laterite?  I've never
seen it anywhere, but I think I'll still use Dupla's laterite (I'm assuming
the high manganese, zinc & copper indexes are good).  This week I noticed
when I gravel vaccuumed in my 25 gal tank that my substrate was anaerobic
(black bits in the gravel & rotten egg smell) - it's due for a change!  It
has been set up for about 18 months.  I lost about 5 mature fancy guppies
in that tank last week but I'm not sure if it was the substrate or my
CO2 & pH problems (boosted CO2 to 22 ppm and pH shot below 6.0 - see below).
All the baby & half grown guppies survived though, as did two cory cats, 
a clown pleco & a kuhli loach.

Re: Vermiculite

I've read or been told that vermiculite is used in house plant potting mix
because it holds water well - probably not neccessary in an aquarium.

Re: pH, KH and CO2

There's a water FAQ that states that for a planted tank pH 6.9, KH 4 and
CO2 15 ppm is just about ideal.  I'm wondering if others aim for this like
I've been trying to do.  I think I have a problem with either my pH or KH
test kit though because at KH 4 (tetra test kit), CO2 15 ppm (La Motte)
my pH is reading 6.4 (Red Sea fish pHarm).  If I increase CO2 to 18 or
higher my pH drops below 6, even with extra teaspoons of baking soda.
This is in a 25 gal tank.

Anyone recomend any better test kits?